Triggering arrangement for a vacuum spark gap



16, 1965 JO EMMETT JENNINGS 3,218,499

TRIGGERING ARRANGEMENT FOR A VACUUM SPARK GAP Filed Dec. 5, 1962 POWER SUPPLY INVENTQR. JO EMMETT JENNINGS AGENT United States Patent 3,218,499 TRIGGERING ARRANGEMENT FOR A VACUUM SPARK GAP Jo Emmett Jennings, La Selva Beach, Calif., assignor to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of Delaware Filed Dec. 5, 1962, Ser. No. 242,436

Claims. (Cl. 313-152) The invention relates to discharge devices, and particularly to a vacuum spark gap device incorporating ignitor means for triggering the spark gap.

Spark gaps and other types of discharge devices are used extensively to discharge stored electrical energy as from a capacitor bank. It has always been a problem to design a discharge device capable of safely handling the enormous amounts of electrical energy capable of being stored in a capacitor bank. As a consequence, the limitations imposed by the discharge device have been an important factor in determining the extent to which a given capacitor bank is charged. It is therefore a principal object of the present invention to provide a vacuum discharge device capable of handling a discharge on the order of one-half million amperes of direct current.

Conventional spark gaps are often characterized by instability resulting from misfiring due to gas current carried by the ionized gases within the evacuated envelope. This instability has made it difficult to accurately control the voltage at which the spark gap will discharge. It is therefore another important object of the invention to provide a vacuum spark gap incorporating controlled triggering or ignitor means to accurately initiate the primary discharge of the device.

Another problem encountered with conventional discharge devices stems from pointed electrodes such as graphite and tungsten electrodes which have been used to trigger the primary discharge. It is customary, for instance, to apply high voltage pulses, generally between 50 to 100 kv. to such pointed triggering electrodes to start the primary discharge. It has been found however that the pointed end of the trigger electrode becomes contaminated by vaporized electrode material, erodes, or otherwise changes its relationship with respect to the primary electrodes and therefore changes the firing characteristics of the main device. For this reason it is still another object of the invention to provide a triggering electrode related to the primary electrodes in a manner to minimize contamination and erosion of the triggering electrodes.

In a vacuum spark gap such as the one herein described, another problem concerns the maintainance of a nonconductive path between opposing electrodes except through an arc in the gap between the electrodes. Because high energy levels are involved, there is a tendency to vaporize electrode material from opposed electrodes when the arc occurs, and this hot vaporized material will condense on adjacent cooler surfaces, both dielectric and metallic, unless prevented. It is therefore a still further object of the invention to provide a spark gap in which shield means are provided insuring against the deposit of a continuous conductive layer of vaporized electrode material on the envelope wall between opposed electrodes.

Because of the enormous amount of electrical energy which the spark gap is designed to handle, tremendous forces are imposed tending to rupture the envelope containing the discharge. It is therefore another object of the invention to provide a metallic and dielectric envelope construction capable of withstanding the tremendous forces thus imposed.

One of the limitations imposed by conventional spark ice I gaps has been the inability to trigger the discharge of the device with any reasonable degree of rapidity. It is accordingly another object of the invention to provide a spark gap in which rapid alternating triggering can be effected.

A still further object of the invention is the provision in a spark gap device of a triggering mechanism which operates with a low voltage on the order of about volts.

Still another object of the invention is the provision of a spark gap in which the envelope may be maintained at ground potential to make the triggering action safe as possible.

The invention possesses other objects and features of advantage some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited by the said description and the drawings but may be embodied in various forms within the scope of the appended claims.

Broadly considered, the vacuum spark gap of the invention comprises an evacuated envelope including metallic and dielectric portions coaxially arranged end-toend and hermetically united to provide a hollow discharge chamber closed at apposite ends by rigid end plates brazed across remote ends of the metallic and dielectric envelope portions. Each of the end plates is preferably fabricated from a non-magnetic material such as copper. Centrally disposed on each end plate is a fixed electrode coaxially arranged with respect to the enclosing envelope portion and including a cylindrical support stem and a disc-like discharge plate mounted on the end of each support stem remote from the end plate. The discharge plates are axially spaced to provide a discharge gap therebetween. Mounted on the envelope is a triggering assembly including an auxiliary housing supporting a solenoid having an armature actuated by electric current passing through a suitable coil. Mounted on the armature and extending into the envelope is a triggering electrode moveable into and out of contact with one of the discharge plates. In the embodiment illustrated in the drawing the triggering electrode is adapted to be in a normally closed position in which the end of the electrode is in physical contact with the associated discharge plate. Upon energizing the coil, current is conducted serially through the coil and the triggering electrode to charge the triggering electrode and simultaneously pull it away from the associated discharge plate, thereby initiating a low voltage are between the triggering electrode and the discharge plate which low voltage are triggers the main discharge. Means are provided within the evacuated envelope to prevent the deposit of vaporized discharge plate material on the adjacent dielectric wall portion of the envelope to prevent formation thereon of a conductive path between the opposing discharge plates.

Referring to the drawings:

FIG. 1 is a vertical cross-sectional view of one embodiment of the invention.

FIG. 2 is a fragmentary sectional view illustrating another embodiment of the invention.

FIGS. 1 and 2 are shown approximately three-fourths actual size.

In terms of greater detail, the vacuum discharge device of the invention comprises a vacuum envelope designated generally by the numeral 2, and including an annular metallic portion having a cylindrical wall 3 provided with radially inwardly extending flange portions 4 and 6 at opposite ends thereof as shown to provide rigidity and a convenient mounting means. For facility of fabrication, cylindrical wall portion 3 is fabricated in two parts having adjacent edges rabbetted to provide a lapped joint suitably brazed to provide a rigid and hermetic wall structure. The metallic wall portion is preferably fabricated from heavy gauge copper.

Hermetically brazed to an inner peripheral portion 7 of flange 6 is a coaxially disposed dielectric envelope portion 8, preferably fabricated from ceramic and flexibly united to the flange by a thin metallic sealing ring including a cylindrical portion 9 having one end brazed to the flange, and a radially inwardly extending annular plate portion 12 brazed across. the end of ceramic member 8. The annular plate portion 12 is supported in spaced and transversely movable relation with respect to flange portion 7 by ceramic backing member 13 brazed to flange 12 as shown.

The other end of the ceramic member 8 is similarly hermetically and flexibly brazed through sealing flange 14 to the adjacent heavy metallic end plate 16 closing the end of the tubular ceramic member 8. End plate 16 is provided with a radially outwardly extending portion 17 having mounting holes therein. Rigidly fixed on the inner face 19 of end plate 16 is a centrally disposed support stem 21,-preferably of copper, having on its inner end a transversely disposed main discharge plate 22, preferably fabricated from tungsten, and rigidly brazed or otherwise secured to the support stem. In one specimen of the discharge device constructed as shown, the discharge plate was approximately 3 in diameter and A" thick.

The other end of the envelope is closed by a heavy metallic plate 23 hermetically united directly to the inner peripheral portion 24 of flange 4 as by brazing. End plate 23, in the embodiment shown in FIG. 1, is provided with a central aperture 26, and from its inner face 27 a support stem 28 extends into the envelope in axial alignment with the support stem 21. Support stem 28 is conveniently tubular in form, having a central bore 29, and is provided on its inner free end with an annular flat discharge plate 31, preferably fabricated from tungsten in the same manner as opposing discharge plate 22. As shown in the drawing, discharge plates 22 and 31 are axially spaced apart to provide a discharge gap 32 therebetween.

Mounted on end plate 23 is a triggering mechanism designated generally by the numeral 33, and comprising an auxiliary housing 34 of ceramic hermetically brazed to plate 23 by annular metallic sealing flange 36. The other end of ceramic member 34 is also provided with an annular metallic sealing member 37 brazed across the end of the housing. The sealing member 37 is provided with a radially outwardly extending peripheral edge portion 38 to which is hermetically bonded an annular metallic support plate 39. The support plate has brazed within its inner periphery a tubular ferromagnetic housing 41, closed at its inner end by end wall 42 and having a centrally disposed magnetic core 43 fixed thereon. The annular space between the core and the housing encloses a suitable electromagnetic coil 44 secured therein by end cap 46 'detachably closing the open end of the housing. It will thus be seen that the housing member 41, sealing member 37, and end wall 42 provide vacuum tight wall portions of the auxiliary housing 34, the interior 47 of which communicates through aperture 26 with the interior of the main envelope 2.

Movably mounted within the chamber 47 contained within auxiliary housing 34 is an armature 48 having an electrically conductive trigger electrode 49 supported thereon and projecting through aperture 26 and central bore 29 in support stem 28. The free end of the conductive trigger electrode is normally maintained in physical contact with the associated discharge plate 31 by a spring 51 interposed between the armature and wall 42 on which the armature is hinged. It will be seen that when coil 44 is energized the armature is pulled against wall 42, thus causing the free end of the trigger electrode to disengage itself from the associated plate electrode 31.

In order to simultaneously break the contact between the trigger electrode and the discharge plate electrode, the

coil and trigger electrode are connected in series through a power supply 52 controlled by a switch 53. Thus, assuming that the metallic envelope portion is at ground potential, closing of the switch 53 causes current to flow serially through the coil and trigger electrode so that as the trigger electrode breaks contact with the associated plate electrode 31, the potential imposed by the power supply initiates a low voltage spark across the broadening gap between the free end of the trigger electrode and the plate electrode. The eflfect of this low voltage are is to trigger the primary discharge between main discharge plate electrodes 22 and 31 which, once commenced, increases rapidly to equalize the potential on opposite sides of the gap. The are discharge between the main discharge plate electrodes will continue until the voltage of the capacitor bank being discharged falls below the ionizing potential of the gases generated by the are. When the discharge has ceased it is then safe to recharge the capacitor bank with the trigger electrode readjusted to its normal position in contact with the associated main discharge plate.

When the primary discharge occurs, the arc will tend to vaporize tungsten from the main electrode plates, and such vaporized tungsten, unless prevented, will be deposited on the relatively cooler inner periphery of the tubular ceramic member 8. To insure that such vaporized metal will not reach the ceramic member 8, a pair of annular metallic baflies are provided within the envelope interposed between the source of such vaporized metal and ceramic member 8. One of the baffles comprises a cylindrical shell portion 54 having one end brazed to the relatively cool flange 6. At its other end this battle is provided with a radially inwardly extending portion 56 having an inner periphery of a diameter slightly larger than the diameter of adjacent plate electrode 22. The second bafile of the pair constitutes an annular plate 57 having its inner periphery brazed to support stem 21 at some distance from plate 22 and having an outer periphery of a diameter slightly less than the diameter of flange portion 7 and tubular ceramic member 8. As shown in FIG. 1, baffie plate 57 is axially spaced below flange portion 56, and, with reference to gap 32, cooperates therewith to provide a tortuous path which has to be transversed by vaporized metal before it can be deposited on ceramic member 8. Experience has shown that such material will be deposited and condense instead on the adjacent metallic envelope portion 3 and the relatively cool baffles.

From the foregoing it will readily be seen that disassembly of the envelope to separate the ceramic portion 8 from the metallic portion 3 may be eflected by break- 1ng the seal between sealing flange 9 and envelope flange 6. End plate 16, with attached support stem 21 and baflle plate 57, may then be extracted from the envelope, the proportions of the baflie plate and the inner periphery of peripheral portion 7 being such as to permit passage of the baffle through the flange 6. This cooperative relationship of the parts enables salvaging of expensive parts of the device.

In the embodiment of the invention illustrated in FIG. 2, the central bore has been eliminated from the support stem 28 and the triggering mechanism has been moved laterally to adjacent one peripheral edge of the end plate 23. Aperture 26 has been repositioned to permit extension of the trigger electrode into close proximity to the outer peripheral edge portion of plate electrode 31. While it would be feasible to have the trigger electrode contact the extreme outer peripheral edge 58 of the plate electrode, it is preferred that an aperture 59 be provided in the plate adjacent its outer periphery. The free end of the trigger electrode then extends into the aperture and is thus shielded from erosion and the deposit thereon of vaporized metal from the adjacent plate electrodes. The operation of this embodiment of the spark gap is similar to the embodiment illustrated in FIG. 1.

To evacuate the envelope, support stem 21 is provided with a transversely extending passage way 61 communicating with tubulation 62 hermetically brazed in end plate 16. The nipped-off end of the tubulation is protected by a cap 63 brazed to the end plate.

Under certain circumstances it may be desirable to control the movement of the are formed by the primary discharge between plates 22 and 31. One satisfactory means for eifecting such control is to fabricate the metallic portion 3 of the envelope from a non-magnetic material such as copper and surround this portion of the envelope with an electromagnetic coil 66 shown in dashlines in FIG. 1. In lieu of an electromagnetic coil, permanent magnets may be arranged about the outer periphery of the envelope in any suitable pattern to provide the desired movement of the arc. Thus, in the embodiment illustrated in FIG. 2, since the arc discharge between the main discharge plates is initiated adjacent their outer periphery, the electromagnetic coil 66 or permanent magnets may be arranged to drive the arc in a circular path adjacent the outer periphery of the plates. In the embodiment shown in FIG. 1, on the other hand, the arrangement of arc control means may be such as to drive the arc radially outwardly toward the outer periphery of the plates, thence circularly about the outer periphery of the plates. The importance of controlling movement of the arc of course is founded on the desirability of maintaining the plates as cool as possible so as to minimize vaporization of material therefrom. It has been found that hundreds of operations, each discharging hundreds of thousands of amperes of electric current, may occur without any serious change in the operating characteristics of the discharge device due to erosion of the main discharge plate electrodes.

I claim:

1. A vacuum discharge device comprising an hermetically sealed envelope, a pair of relatively equally vaporizable opposed main electrodes supported within the envelope in electrically insulated spaced relation to provide a gap therebetween across which an arc may strike, and a triggering mechanism mounted on the envelope and including an electrically changeable triggering electrode within the envelope selectively moveable into and out of contact with one of the electrodes to initiate an arc discharge between the main electrodes.

2. The combination according to claim 1, in which shield means are provided within the envelope interposed between said gap and the interior surface of an adjacent section of the envelope wall to shield that section of the envelope from the deposit thereon of vaporized metal.

3. The combination according to claim 1, in which the triggering mechanism includes a hollow evacuated auxiliary housing, a magnetizable armature moveably mounted within the evacuated auxiliary housing and an energizable coil supported on the housing to move the armature and said triggering electrode when the coil is energized.

4. The combination according to claim 1, in which the envelope comprises tubular metallic and dielectric portions disposed end-to-end, flexible metallic sealing means heremtically uniting adjacent ends of the tubular metallic and dielectric portions to compensate differences in thermal expansion and contraction therebetween, and metallic end plates heremtically closing the remote ends of the tubular metallic and dielectric envelope portions.

5. The combination according to claim I, in which said envelope is fabricated from non-magnetic material.

6. The combination according to claim 1, in which each main electrode includes an electrically conductive support stem fixed by one of its ends on the associated end of the envelope and a circular metallic discharge plate fixed on the other end of the support stem remote from the associated end of the envelope, said discharge plate lying parallel to the discharge plate of the opposite electrode in all positions of the envelope.

7. The combination according to claim 5, in which means are provided surrounding the non-magnetic envelope to generate a magnetic field having flux lines oriented with respect to the field generated by the main discharge are in a manner to drive the arc in a predetermined path within the gap.

'8. A discharge device comprising an hermetically sealed envelope, a pair of opposed main electrodes supported within the envelope in electrically insulated spaced relation to provide a gap therebetween across which an arc may strike, each said main electrode including an electrically conductive support stem fixed by one of its ends on the associated end of the envelope and a circular metallic discharge plate fixed on the other end of the support stem, said discharge plate lying parallel to the discharge plate of the opposite electrode, and a triggering mechanism mounted on the envelope and including an electrically chargeable triggering electrode within the envelope selectively movable into and out of contact with one of the electrodes to initiate an arc discharge between the main electrodes, one of said main electrode support stems and the associated discharge plate being centrally apertured and the triggering electrode extending through the apertures into operative association with the inner periphery of the discharge plate.

'9. A discharge device comprising an hermetically sealed envelope, a pair of opposed main electrodes supported within the envelope in electrically insulated spaced relation to provide a gap therebetween across which an arc may strike, each said main electrode including an electrically conductive support stem fixed by one of its ends on the associated end of the envelope and a circular metallic discharge plate fixed on the other end of the support stem, said discharge plate lying parallel to the discharge plate of the opposite electrode, and a triggering mechanism mounted on the envelope and including an electrically chargeable triggering electrode within the envelope selectively movable into and out of contact with one of the electrodes to initiate an arc discharge between the main electrodes, one of the discharge plates being apertured adjacent its outer periphery and the triggering electrode operatively associated therewith extending into the aperture and movable to make and break contact with the periphery of aperture.

10. A discharge device comprising an hermetically sealed envelope including tubular metallic and dielectric portions disposed end-to-end with adjacent ends thereof hermetically united and remote ends thereof her-metically closed 'by metallic end plates, a pair of opposed main electrodes supported within the envelope in electrically spaced relation to provide a gap therebetween across which an arc may strike, each said main electrode including an electrically conductive support stern fixed by one of its ends on the associated metallic end plate of the envelope and a metallic dischrage plate fixed on the other end of the support stem, said discharge plates lying in spaced parallel relation to define said gap, shield means within the envelope interposed between the gap and the tubular dielectric portion of the envelope to shield the dielectric portion from the deposit thereon of vaporized electrode metal, said shield means including a pair of spaced and electrically insulated annular baflle plates the outer periphery of one of which is fixed on the tubular metallic envelope portion and the inner periphery of the other of which is fixed on the adjacent main electrode, and triggering mechanism mounted on the envelope and including a hollow housing, a magnetizable armature movably mounted on the housing, an electrically charge- 7 8 able triggering electrode supported on the armature and References Cited by the Examiner extending into the envelope and selectively movable into UNITED STATES PATENTS and out of contact with one of the mam electrodes to 2151979 3/1939 Lems 313 152 initiate an arc discharge between the main electrodes, and an energizable electromagnetic coil supported on the 5 2,49 015 42 12/1949 Read 313156 housing and serially connected in circuit with the triggering electrode to simultaneously move and charge the elec- GEORGE WESTBY Pnmary Examme" trode when the coil is energized. 

1. A VACUUM DISCHARGE DEVICE COMPRISING AN HERMETICALLY SEALED ENVELOPE, A PAIR OF RELATIVELY EQUALLY VAPORIZABLE OPPOSED MAIN ELECTRODES SUPPORTED WITHIN THE ENVELOPE IN ELECTRICALLY INSULATED SPACED RELATION TO PROVIDE A GAP THEREBETWEEN ACROSS WHICH IN ARC MAY STRIKE, AND A TRIGGERING MECHANISM MOUNTED ON THE ENVELOPE AND INCLUDING AN ELECTRICALLY CHARGEABLE TRIGGERING ELECTRODE WITHIN THE ENVELOPE SELECTIVELY MOVEABLE INTO AND OUT OF CONTACT WITH ONE OF THE ELECTRODES TO INITIATE AN ARC DISCHARGE BETWEEN THE MAIN ELECTRODES. 